hmm, good to hear wet battery is worth the extra expense! as far as i know, yes it'll be better to get higher Ah battery. so u can get the max Ah available within the size limitation.
on tyre size, 195/50/R15 will result in almost the same effective size as the factory fitted ones (155/80/R13)... so won't change the height. u'll just end up buying newer rims and also end up with slightly reduced shock absorbing capability.
raising up your car... i believe the car manufacturer would recommend getting the springs changed to slightly harder and larger ones instead of spacers (rubber or metal). if u can wait a month, i'm planning on visiting khi during eid holidays, will show u the place from where i got my springs in plaza. they already had springs made for different cars (similar to how cache got his) and they gave a year's warranty as well! after buying them i got them changed from this place right beside Friends CNG's workshop (Baloch colony) and he did an okay job.
metallic vs. rubber spacers - from experience of various ppl, metallic ones can squeak! and rubber ones later on become problematic as with time they compress and one side's spacer might compress more than the other!
i just changed my rear springs and did not need to touch the front at all. with cng, i don't hit speed breakers any more - and the car doesn't look extra "high" either.
dude, cng is not recommended for any petrol car. simple. but just for the sake saving some money, we have to compromise on a few things. if u can afford petrol, then it's better u avoid cng. if not, then join the club! just do some research and don't try to save money in getting cng conversion.
if u've recently bought the car, i'd recommend driving it for a couple of months and making sure everything else is working well before going with cng kit.
pal.. i've heard the vitz fuel filter does not need replacement unless there's some serious issue with it. i think u shud just get it cleaned, if needed. rest of the things should be changed (on their respective times). goodluck with the royal shielding!
(btw is it just me or is it really too complicated to keep track of all forums on pw?)